Ultra shower cartridge replacement

[Vincennes26]

I purchased a house recently so know noting of the installation of the shower in my ensuite There are two shower heads, each controlled by it's own 1/4 turn on/off valve but with a single mixer valve for temperature.

One of the shower heads recently started dripping. I assume the cartridge needs replacing but have had a really difficult time identifying the maker of the valves (the shower head says Moen but I know it's not a Moen valve assembly).

After much searching, I believe the valve assembly is made by a company called Ultra and the cartridge is part number SVR21W

Of course the logical step is to verify this by removing the old cartridge and thats where my problem is. The old cartridge appears to be threaded in. I've used a 17mm socket to try and remove it but it's just starting to strip the nut.

Any tips on getting this thing out? I'm hoping to avoid removing the faceplate because it's silicone sealed on.

Thanks.

 

[havasu]

I'd remove the silicone and take off the face plate, so you could get a good grip on the cartridge before you round the edges, ending up buying an entire new unit.

 

[DFBonnett]

It looks like it might come off with a deep well socket.

 

[Vincennes26]

Hi there, I had tried a deep well socket 17mm and it was fitting around the bolt but still rounding the edges when I tried applying force.

I removed the face plate as suggested. Previous owner used WAAAAAYYY too much silicone. Anyway here's a pic of whats underneath. No marking to indicate manufacturer. Still unable to get a wrench on the top bolt at the base of the long shaft and turn without it starting to strip. Tried pulling and wiggling... nothing.

Maybe some sort of penetrating lubricant? Or maybe I've got this all wrong and it's supposed to be removed a completely different way.

UPDATE: I removed the bottom cartridge without difficulty. It is threaded and it is 17mm (see pic). The top one is therefore seized. I tried spraying it with penetrating lube, deep 17mm socket and I even tried an impact wrench (I'm sure that'll attract some criticism). Unfortunately none have worked and the stripping is getting worse the more I try (no, the impact gun didn't strip the nut, it was trying to use the deep socket).

So now what???

Thanks